1. Field of the Invention
This invention relates to solventless, fast-setting, anaerobic adhesive composition for bonding together two or more substrates by anaerobic polymerization.
2. Description of the Prior Art
The phenomenon of anaerobic polymerization is one that is well known in the art and one which is readily effected in commercial practice by interposing an adhesive composition between two opposing substrate surfaces that are to be bonded together with such adhesive composition. Upon such substrate surfaces being pressed together, air is thereby excluded, giving rise to rapid polymerization of the adhesive composition which, in turn, causes the two substrates to be bonded via the resultant polymerized adhesive composition.
The use of acrylate monomers for this purpose is well known and described in a number of prior U.S. patents, such as U.S. Pat. Nos. 3,419,512, 3,425,988 and 3,435,012. For example, U.S. Pat. No. 3,419,512 discloses anaerobic adhesive compositions comprising monomers of dimethylacrylate or diacrylate esters of polyglycols, an organic peroxide polymerization initiator, water, an acid or acid salt, and, optionally, an organic tertiary amine and a plasticizer, and teaches that such compositions are capable of attaining a range of specified bond strengths within rapid setting times. U.S. Pat. No. 3,425,988 relates to polyurethane-polyacrylate sealant compositions comprising the reaction product of an acrylate ester, an organic polyisocyanate and a peroxy polymerization initiator, which compositions polymerize when placed between non-porous substrate surfaces.
Previous bonding processes, such as those above, that have been characterized by interposing a polymerizable adhesive composition between a plurality of substrates, or by applying an adhesive composition to the surface of one substrate and then pressure contacting the resultant adhesive-containing substrate surface to a second substrate, have frequently given rise to inferior products that have been characterized by non-uniform bond strength, owing to slight variations in thickness and the like of the intermediate adhesive layer, or decreased bond strength of the resultant bonded material over a moderate time span such as a month. Furthermore, such prior art processes have quite often required the use of solvents in order to promote bonding or to "activate" the substrate surfaces. Such solvents have often proved to be undesirable, both from pollution and fire hazard standpoints, and for use in bonding solvent impervious surfaces.
Accordingly, it is an object of the present invention to provide new and improved solventless, fast-setting anaerobic adhesive compositions which are capable of forming high-strength bonds to substrate surfaces at ambient temperatures.